noun

• (botany) In bryophytes, a thin, hood of tissue that forms from the archegonium and covers the developing sporophyte and is shed as it ripens.
• (botany) any cap-like covering of a flower or fruit, such as the operculum over the unopened buds of Eucalyptus flowers
• (botany) Any of various coverings at the tips of structures, in the terminology of various authors; for example rootcaps and the apical cells of trichomes.
• (entomology) In flies such as the housefly, Musca, in the taxonomic order Diptera, zoological section Schizophora, subsection Calyptrata, the calyptra is a membranous rearward extension of the forewing; it covers the haltere.